OET is life-saving for women with estrogen receptor-positive (ER+) breast cancer because it reduces the incidence of recurrence and mortality. OET adherence is not a single event decision, but rather is a psychosocial process unfolding over time involving an initial decision to initiate therapy or not, and for those who do initiate OET, several additional decisions. These include (1) ongoing daily or twice-daily decisions to continue to ingest pills, (2) decisions about whether to switch to a different OET if the first is not tolerted, and (3) decisions about whether to stop the therapy altogether. Our understanding of OET decision making is limited, but non-adherence is a common response to OET side effects. By obtaining first-person narratives from women who have been prescribed OET and report experiencing side effects, an explanatory framework can be developed that describes their decision making processes. In particular, salient decisional needs and decisional supports sought by or provided to the women over time can be highlighted in the framework. This framework can then be used in the future to develop interventions, such as decision aids, to promote quality decision making and better health care for women. Therefore, the purpose of this grounded theory study is to develop an explanatory framework of decision making by women with ER+ breast cancer who report experiencing OET side effects. Specific aims are to (1) describe responses to side effects among women with ER+ breast cancer , (2) identify common decisional needs of women with ER+ breast cancer who report experiencing OET side effects, (3) identify common decisional supports sought by and provided to women with ER+ breast cancer who report experiencing OET side effects, and (4) describe how women with ER+ breast cancer who report experiencing OET side effects make decisions about initiating, continuing, switching, and/or discontinuing OET. In this study, 30 women with ER+ breast cancer who report experiencing OET side effects will take part in a single, face-to-face, audio-recorded interview. Demographic and breast cancer treatment information will be collected and then analyzed using descriptive statistics. A constant comparative method of inductive and deductive processes will be used to discover common patterns and variations in the narrative data. The final products of the analysis will include typologies of responses to side effects, common decisional needs, and common decisional support as well as a framework of common trajectories of decision making related to OET in women who report experiencing side effects.